Subarachnoid-Pressure-Dependent Drug Effects on CSF Transport and Brain Volume

Abstract

Cats or rabbits anaesthetized with Nembutal or Urethan were fixed in a stereotactor, the head in an upright position. A small burr hole was drilled into the skull so that thin tubes of varying lengths could be fixed vertically into the burr hole near to the crossing of the sagittal and coronary sutures. The system was made watertight. The dura in the burr hole was opened. Mock CSF was filled into the vertical tube and the rate of its disappearance was plotted against the hydrostatic pressure. Pressure was increased from 0.5–8 cm H₂O. In this pressure-range the degree of resorbed CSF fluid is linearily dependent on the CSF pressure and even small increases in CSF pressure cause an increase in CSF-resorption [1]. From experiments by Heisey et al. [2] and Bering and Sato [3] it can be concluded that the production of CSF is not significantly changed during such small increases in CSF pressure. Therefore, it seems to us that the disappearance of mock CSF is caused by resorption. The brain volume was recorded with a device consisting of a very light displacement transducer within the tube fixed on the skull. It is possible to take the change in vertical displacement of one point in the brain as a relative measure of its volume variation. According to the law of similar bodies, the volume variations of such bodies are equal to the cubes of their lengths. Thus the vertical displacement of the surface is a relative measure of the brain volume. The displacement transducer was watertight to prevent an escape of fluid.